A method of making urea-containing particles is known from U.S. Pat. No. 7,700,012. Therein the urea comprising particles are produced in a pelletizer comprising a feeding device, a belt and a device to remove the formed pellets from the belt, by feeding a urea comprising liquid to the feeding device from which droplets of the urea comprising liquid are dosed to the belt. Thereon the urea comprising droplets solidify and cool to a temperature which is required to be 55° C. or lower, after which the formed urea comprising particles are removed from the belt. The cooling to below 55° C. is taught to be essential in order to obtain the necessary mechanical strength to handle the particles and to prevent abrasion and dust formation. Although this is significantly below the melting temperature of urea (around 132° C.), above 55° C. the granulate does not have enough strength, is more sticky and generates dust. The stickiness leads to fouling of the equipment and consequently lower on stream times. This temperature requirement leads in practice to very large and costly equipment due to the required residence time on the belt and at the same time restricts the size of the droplets to be formed. Alternatively it leads to the need for a very low temperature cooling medium, e.g. liquid nitrogen, which adds to operating cost.
Another reference relating to particles comprising urea is U.S. Pat. No. 7,931,729. The latter reference does not address mechanical strength of urea-comprising particles. Rather, it addresses an issue related to the use of urea as a fertilizer, by providing controlled release fertilizer particles in the form of polymer-encapsulated fertilizer, such as urea. To this end, the fertilizer is deposited onto a first polymer film and then covered by a second polymer film to encapsulate the fertilizer between the first polymer film and the second polymer film. The method can be carried out on a rotoformer, which is a device with a moving belt, a feeding device, feeding droplets onto the belt, wherein the belt is cooled. The cooling of the fertilizer droplets is disclosed to be to room temperature, i.e. as is convention in accordance with U.S. Pat. No. 7,700,012. The cooling of the fertilizer makes it easier to cut apart the encapsulated fertilizer droplets.
It would be desired to provide urea-containing particles that have a mechanical strength, and absence of dust formation, at least at about the level of the particles formed by cooling in U.S. Pat. No. 7,700,012. Yet, it would be desired to be able to avoid the aforementioned drawbacks of the cooling as disclosed.